The present invention relates to a contact lens storage container, and more particularly relates to a storage container for a soft hydrophilic contact lens.
Soft hydrophilic contact lenses are generally manufactured from hydrophilic polymer material. Depending on the composition of the polymer, the lenses may have a water content of from 20 percent to 90 percent or more. Such contact lenses must be preserved and stored in a liquid such as a sterile aqueous solution, usually an isotonic saline solution, to prevent them from drying out and to maintain them in a state ready for use.
Contact lenses have two curved surfaces with a circular edge in between. The surface that contacts the user's eyeball is called the base surface. The base surface cannot usually be defined m by a portion of a perfect sphere because the front of the human eyeball to which the base surface conforms is not perfectly spherical. Thus, the base surface cannot be defined by a single radius along its entire surface. However, a base curve equivalent radius is commonly used to approximate the radius of the base surface. The base curve equivalent radius is determined by a curvefitting calculation to derive an effective equivalent radius of the base surface from its complex shape.
Typical base curve equivalent radius sizes in use today include 8.2, 8.4, 8.6, 8.8, and 9.0 millimeters, with 8.4 and 8.8 millimeters being the most common. These sizes are arbitrarily chosen within the range of sizes that fits most people's eyeballs. Any size within the 8.2 to 9.0 millimeter range, and even smaller or larger sizes, is suitable for at least some people. The commonly-used sizes are chosen to reduce the number of different types of lenses that must be manufactured and inventoried to an amount small enough to safely and comfortably fit the vast majority of people that may be contact lens wearers.
The surface of the contact lens opposite the base surface is the front surface. The front surface typically has a more irregular surface than the base surface, as the variation in thickness of a contact lens that causes correction of vision is made relative to the base surface, which is sized to fit the user's eyeball. Typically, the front surface of a lens has three concentric areas, each having a different radius: a circular central optic zone, an annular outer edge zone, and an annular lenticular zone between the optic zone and the edge zone. Due to the high refractivity of the contact lens material, the variation in thickness required to correct vision is slight (on the order of about 80 microns). However, in view of the shapes of the base surface and the front surface, contact lenses are typically identified according to base curve equivalent radius and optical properties, rather than according to their front surface shape.
Numerous types of containers for storing contact lenses are known, such as those described in U.S. Pat. Nos. 4,392,569; 4,691,820; 5,054,610; 5,409,104; 5,467,868; 5,474,169; and 5,609,246. Known containers all include some sort of a chamber for holding the contact lens and storage liquid, and some sort of a cover for keeping the lens and liquid in the chamber.
U.S. Pat. No. 5,609,246 discloses a contact lens storage container having a chamber formed in two portions. The main portion of the chamber is dish-shaped or bowl-shaped. Also, the main portion is sized so that it can accommodate contact lenses of various sizes, with a diameter of approximately 20 mm at the chamber opening and a depth of approximately 6 mm measured perpendicular to the plane of the opening.
U.S. Pat. No. 5,474,169 discloses a contact lens storage container having a cavity for receiving a lens and liquid, the lens base surface being placed on a post extending upward from a bottom surface of the cavity. The cavity is substantially larger than the lens, and is designed so that a thumb and forefinger can be placed into the cavity on opposite sides of the post for removing the lens from the container.
U.S. Pat. No. 5,467,868 discloses an ophthalmic lens package having a bowl with a radius of curvature greater than that of the front surface of a contact lens such that the lens settles to the bottom center of the bowl when placed in the package. The preferred bowl radius of curvature is stated to be 9.5 mm, with 9.5 to 12.0 mm being a preferred range. The bowl is intentionally sized so that the contact lens only touches the bowl at one point, and no line or surface contact between the lens or bowl occurs, as clearly shown in FIG. 3 of that patent. Thus, the lens is free to move about the bowl as the package is moved. If the package is held upright, the lens settles at the center (bottom) of the bowl, but does not adhere to the bowl.
Recently, new types of silicone based hydrogel contact lenses have been developed that can have memory characteristics. If this type of contact lens is held in a position different from its normal bowl-shaped position, the shape of the lens may be changed by a small amount. For example, folding of the lens in half or inverting of the lens may change its shape. While the storage containers disclosed in the above patents work well for use with conventional contact lenses, it is possible that these and other storage containers might allow contact lenses to change shape while in storage or transit to an ultimate user.
During manufacture of contact lenses, lens inspection is often performed by visually detecting and observing each lens after placement in the storage liquid in the container. Often, the container is made at least partially translucent so that the lens may be inspected through the chamber wall after the cover is placed over the chamber. Inspecting a contact lens in the chamber, whether one of the hydrogel lenses described above or a conventional lens, may be difficult or impossible if the lens is curled or inverted.
Typical prior art contact lens containers have chambers substantially larger than the lenses. Thus, locating a clear contact lens in a clear storage solution within the chamber may be difficult during manufacture, inspection, or use by the user, especially if the lens has moved away from the bottom of the chamber. For example, inspection of a contact lens may be impossible if the lens is not at the chamber bottom. Also, a user may have to feel around the chamber with a finger to locate the contact lens, which could possibly lead to inadvertent loss or tearing of the lens in some situations.
In addition, it has been found that the silicone hydrogel lens will stick to the bowl of the container when the radius of the container closely approximates the radius of the lens. There is therefor a need to find a way to modify the bowl of the container to prevent adhesion of the silicone hydrogel lens to the bowl.